One example of the flat displays for current driving is a Field Emission Display (hereinafter referred to as an "FED"), and the present invention proposes an improved data driving device of the field emission display using a passive matrix addressing method,.
What has been spot-lighted as a flat display is a Liquid Crystal Display (LCD), which displays image by interrupting beam from the light source using liquid. The driving method thereof is largely divided into a passive matrix addressing method and an active matrix addressing method. The passive matrix addressing method of the LCD is that different voltages are applied to the upper and lower plates of the glass substrate of the LCD, respectively, thus inputting the data to the pixel at the crossing point. This method has a disadvantage in that the adjacent pixels of the designated pixel are also affected and thus a compensating circuit for fine picture is required, resulting in a complicated driving device. The active matrix addressing method is that one pixel has a cell transistor and a capacitor and one pixel is continuously driven by the previous pixel data until the following pixel data is input, and this method permits an improved definition and a simplicity of the driving device. However, the active matrix addressing method is disadvantageous in that it requires a plurality of transistors and capacitors on the glass substrate of the LCD, thus resulting in a complicated manufacturing process and low yield. The LCD now occupies the largest part of the flat display market. However, it has some problems in that only several percentage of light from the light source actually affects the picture, resulting in greater power consumption and difficulty in large-scale area. Also, since semi-liquid material (liquid crystal) is used, the LCD is sensitive to the temperature change, weak in input, has a dark picture and a limit in resolution. In order to solve these problems, research is being conducted on the FED as a substitute flat display. The FED displays picture in a similar manner as the cathode-ray tube which displays image using the emitted electrons. However, the FED is different from the cathode-ray tube in that the FED uses Cold Electron Emission while the cachode-ray tube uses Thermal Electron Emission.
In FED, the field emission elements which emit electrons are placed at every pixel and the electrons from the field emission elements are collided with the electrode doped with fluorescent film, thus displaying the image. The FED is now being spot-lighted as a next generation flat display which can solve the above problems of the LCD.
The FED can integrate several hundreds or several thousands of field emission elements to form one pixel. Each of the field emission elements constituting the pixel of the FED has a cathode 12 connected to a cathode electrode 10, a gate electrode 14 separately arranged over the cathode 12 by a predetermined interval, and a positive plate 18, as shown in FIG. 1. The rear surface of the positive plate 18 is doped with a fluorescent film 16. The fluorescent film 16 generates light corresponding to the amount of the collided electrons, thus enabling the display of the image. The positive plate 18 serves to attract the electrons emitted from the cathode 12 and is made to be transparent so that the light from the fluorescent film 16 can be transmitted. The cathode 12 is of the horn type with a pointed part and emits electrons from the pointed part thereof by the driving power from the cathode electrode 10. The gate electrode 14 has a hole to expose the pointed part of the cathode 12. The gate electrode 14 makes the electrons to be emitted from the cathode 12 by the high voltage lower than the voltage applied to the positive plate 18, and the positive plate 18 app1ied with the high voltage accelerates the electrons emitted by the gate electrode 14 to the positive plate 18.
FIG. 2 illustrates a passive matrix driving device according to a prior art. Referring to FIG. 2, gate driving circuits 22a, 22b and 22c are connected to gate lines 14a, 14b and 14c, and cathode driving circuits 24a to 24e are connected to cathode lines 10a to 10e. At the crossing points of the gate lines 14a to 14c and cathode lines 10a to 10e, horn type of field emission elements 12 as shown in FIG. 1 are arranged. A plurality of field emission elements 12 are integrated to constitute one pixel. However, for the convenience of description, it is assumed that one field emission element 12 constitutes one pixel. Thus, FIG. 2. shows the FED having 3.times.5 pixels and the driving device thereof.
Another method for driving the FED, i.e. the active matrix addressing method is disclosed in U.S. Pat. No. 5,210,427 of Micron Technology Inc. In the active matrix addressing method of the Micron Technology Inc., two transistors are connected to each pixel shown in FIG. 2 and the pixel holds the data applied thereto until the following data is applied thereto in a similar manner as the active matrix addressing method of the LCD. The active matrix addressing method of the Micron Technology Inc. is advantageous in that the transistors of each pixel operate at a lower voltage and the control circuit has a simple structure. However, each pixel requires a plurality of transistors, resulting in a complicated manufacturing process. As compared therewith, the passive matrix addressing method of the FED has a simple manufacturing process. However, since it does not have the transistor and capacitor per pixel, the emission of the electrons from one pixel is limited by the length of the pulse which sequentially scans the data lines which are crossed with one gate line applied with a high voltage. The degree of the light emitted by the electrons collided with the fluorescent film 16 doped at the positive plate 18 relates to the amount of the emitted electrons and the energy of the emitted electrons reached the positive plate 18. Since the scan pulse of the cathode lines 10a to 10e of the FED is determined depending upon the system, the field emission element may not emit sufficient electrons during the above scan pulse length.